The present invention relates to extrusion billet quenching systems, and more particularly to such systems for creating a tapered quench in a heated billet.
A conventional nonferrous extrusion system typically includes a billet furnace, an extrusion press, and additional "downstream" equipment to handle the extruded material. Billets or logs are heated in the furnace to a temperature suitable for extrusion. The heated billets are then extruded by the press. Heating homogenizes metallic compounds within the billet and renders the billet suitably plastic for extrusion.
Extrusion press rams operate at a uniform speed for the entire length of a billet to reduce the amount of heat build-up in the billet. The billet exits the furnace typically having a uniform temperature throughout its entire length. As is well known the billet temperature changes during uniform-speed extrusion. Specifically, the rear end of the billet adjacent the press ram heats up as it is forced through the container. This heat is created by the friction between the billet and the container during extrusion. The nonuniform billet temperatures create several problems. First, "hot" extrusions can include tears or surface blemishes. Second, the extrusion die flexes with varying temperatures and pressures creating variations in the extrusion profile. Such flexing makes it impossible to maintain tight tolerances. Therefore, the desirability of providing a temperature gradient throughout at least a portion of the extrusion billet prior to extrusion has long been recognized. If the rear end of the billet has a temperature below that of the forward end when the billet is placed in the press, the temperature of the billet throughout its length will be more uniform during extrusion. Accordingly, the concept of isothermal extrusion, meaning that the temperature of all billet material passing through the die is uniform, has long been recognized as desirable.
One technique of providing the temperature gradient involves the use of induction furnaces having a series of induction heaters along the length of the billet. The induction heaters can be controlled to heat each section of the billet to a different temperature. The rear end of the billet can be heated to a temperature below that of the forward end of the billet. This technique is suitable only with induction heating, which is relatively slow. This technique of providing a temperature gradient is not suited to non-induction-type furnaces.
Granco Clark, Inc., the owner of the present application, has developed three previous techniques for quenching the rear end of the heated billet after it exits the furnace and before it enters the press. The first technique is the use of a water ring that surrounds and is moved manually along the billet. The efficacy of this technique depends on the judgment of a human operator. Unfortunately, this technique often results in the entire billet being cooled a uniform temperature throughout its length. The second technique is spraying water in a longitudinal direction against the rear end of the billet. This technique requires excessive time to quench the rear end. Consequently, the entire billet often cools down; and this technique also is subject to human judgment. The third technique is illustrated in U.S. Pat. No. 5,027,634 to Visser et. al. entitled SOLUTIONIZING TAPER QUENCH. The taper quench includes a water-spray ring and a transport mechanism for moving a billet back and forth through the ring. The transport mechanism operates at a single operator-selected speed for a single operator-selected length. Although an improvement over prior techniques, this technique also is subject to human judgment.